There are 2 files in the NSO documentation that you should to look at. First, the nso_installation_guide covers the standard procedure for upgrading NSO. However, from NSO 5.1 onwards, NSO implements the Common Device Model, or CDM. As a result, you must perform the CDM migration procedure instead of the standard upgrade procedure when upgrading from NSO 4.7 to NSO 126.96.36.199. The details for the migration are contained in the nso_cdm_migration_guide. I recommend reading the migration guide thoroughly before performing the upgrade.